Japanese Provisional Utility Model Publication No. 72325 of 1993 discloses a thread milling cutter with drill blade having a pre-drilling blade at the tip of a thread milling cutter.
This thread milling cutter has a tapping blade in each of the auxiliary lands that are twice as large as the main lands by forming an auxiliary groove in the main lands provided on both sides of the main groove to ensure smooth removal of chips from pre-drilling and efficient accomplishment of subsequent thread cutting.
With this type of thread milling cutters, however, provision of the auxiliary groove inevitably decreases the cross-sectional area of each auxiliary land and thereby reduces the strength of the cutting blades formed therein. Then, stresses set up during high-speed cutting operation would break the thread milling cutter.
The object of this invention is to provide new type of thread milling cutters with drill blade that permit high-speed cutting without breaking.